1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method of performing wireless communication in a multi-carrier system.
2. Related Art
Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data communication. In general, a wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available radio resources. Examples of multiple access systems include a time division multiple access (TDMA) system, a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
In a wireless communication system, one carrier is considered in general even if a bandwidth is differently set between an uplink and a downlink. In the 3rd generation partnership project (3GPP) long term evolution (LTE), one carrier constitutes each of the uplinks and the downlinks on the basis of a single carrier, and the bandwidth of the uplink is symmetrical to the bandwidth of the downlink. However, except for some areas of the world, it is not easy to allocate frequencies of wide bandwidths. Therefore, as a technique for effectively using fragmented small bands, a spectrum aggregation technique is being developed to obtain the same effect as when a band of a logically wide bandwidth is used by physically aggregating a plurality of bands in a frequency domain. The spectrum aggregation includes a technique for supporting a system bandwidth of 100 mega Hertz (MHz) by using multiple carriers even if, for example, the 3GPP LTE supports a bandwidth of up to 20 MHz, and a technique for allocating an asymmetric bandwidth between the uplink and the downlink.
In a multi-carrier system, to transmit and receive downlink data or uplink data or both, a downlink carrier or an uplink carrier or both has to be first configured. In a Frequency Division Duplex (FDD) system, downlink carriers are mapped to respective uplink carriers. Accordingly, if a wireless network changes a downlink carrier used to transmit data for a specific User Equipment (UE) to another downlink carrier, a corresponding uplink carrier has also to be changed. Further, if a wireless network changes an uplink carrier used to receive data from a specific UE to another uplink carrier, a corresponding downlink carrier has also to be changed. In this case, the downlink carrier and the corresponding uplink carrier have to be separately configured, which can cause the overhead for control information to be increased. Accordingly, there is a need for a method of reducing the overhead of control information in a multi-carrier system.